Year 8 Science · Unit 1 · Lesson 21
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Learning Goals
Match each process to what happens
Write the matching letter in the middle column. Each letter is used once.
| Process | Letter | What happens |
|---|---|---|
| Photosynthesis | A. Fungi and bacteria break down dead matter and release nutrients. | |
| Respiration | B. Water vapour cools and turns into tiny droplets that form clouds. | |
| Decomposition | C. Water vapour leaves a plant through its leaves. | |
| Transpiration | D. Living things release carbon dioxide into the air. | |
| Condensation | E. Plants take in carbon dioxide and use it to build sugars. |
Odd one out
In each row, circle the one that does not belong. Give the reason.
| Row | Examples | Reason |
|---|---|---|
| 1 | evaporation · transpiration · photosynthesis · precipitation | |
| 2 | sunlight · calcium · potassium · phosphorus | |
| 3 | carbon in a koala · water vapour in a cloud · carbon in ocean water · carbon in rocks |
1. Name the two processes that move water from the ground and from living things up into the air.
Classify with a reason: matter or energy?
Write “matter” or “energy”, then say whether it is recycled or flows one way, and why.
| Example | Matter or energy? | Recycled or one way? Why? |
|---|---|---|
| Carbon atoms in a gum leaf | ||
| Light from the Sun reaching a fern | ||
| Water vapour given off by a eucalypt | ||
| Heat given off by a rotting log |
Cause and effect: after a bushfire
Complete both cause-and-effect chains. They show two different ways fire can affect plant recovery.
Acacia responses vary by species and fire conditions. Heat can affect hard-seed dormancy; ash nutrients are a separate pathway that may support later growth. In other plant species, smoke may act as a germination cue, but it does not physically weaken a hard seed coat.
Read the data
Investigation: leaf-litter bags
A class put 20 g of dry gum leaves into each of six mesh bags. Three bags were pegged to the ground in a damp, shady gully and three on a dry, sunny ridge. Every two months they dried and weighed the leaves left in one bag from each site.
| Time (months) | Damp gully (g) | Dry ridge (g) |
|---|---|---|
| 0 | 20.0 | 20.0 |
| 2 | 15.0 | 18.5 |
| 4 | 11.0 | 17.0 |
| 6 | 8.0 | 15.5 |
Source: sample class results.
2. What percentage of the leaf mass was lost in the gully bag after 6 months? Show your working.
Answer %
3. Compare the two sites. Suggest why the leaves broke down faster in the gully.
4. A student says: “12 g of leaves vanished from the gully bag.” Explain where that matter really went.
5. Imagine every decomposer in a forest suddenly disappeared. Predict what would happen to the forest floor and to the plants over the next few years.
6. A national park ranger has to decide how often to let small, planned fires burn a patch of bushland. Using nutrient cycling, explain how fire can help the bush recover, why fires that are too frequent or too intense can harm it, and what the ranger should do.
Match each process to what happens
Photosynthesis → E; Respiration → D; Decomposition → A; Transpiration → C; Condensation → B.
Odd one out
Row 1: photosynthesis (not a water-cycle stage). Row 2: sunlight (energy, not a nutrient). Row 3: water vapour in a cloud (not a carbon store).
1. Evaporation (from oceans, rivers and dams) and transpiration (from plants). [2 marks]
Classify with a reason: matter or energy?
Carbon in a leaf: matter, recycled (back to air and soil). Sunlight: energy, one way (lost as heat). Water vapour: matter, recycled (falls as rain). Heat from a log: energy, one way (not reused).
Cause and effect: after a bushfire
Germination chain: for some Acacia species, heat can weaken a hard seed coat, allowing water entry; with suitable conditions the seed may germinate. Nutrient chain: ash returns some mineral nutrients such as potassium, calcium and phosphorus to soil; these may support later seedling growth. They are separate processes, and Acacia responses vary by species and fire conditions.
Read the data
2. Lost = 20.0 − 8.0 = 12.0 g; 12.0 ÷ 20.0 × 100 = 60%. [2 marks: 1 working, 1 answer]
3. Gully lost 12.0 g, ridge 4.5 g; decomposers work better where it is damp. [2 marks: 1 comparison with data, 1 reason about decomposers]
4. Decomposers broke the leaves down: some matter went into the soil as nutrients, some into the air as carbon dioxide. [2 marks]
Show What You Know
5. Dead matter piles up; nutrients stay locked in it; soil runs short and plants grow poorly. [3 marks: 1 dead matter builds up, 1 nutrients not returned, 1 effect on plants]
6. Marking guide: 1 explains that heat can weaken hard seed coats in some Acacia species, allowing water entry, with responses varying; 1 distinguishes this germination cue from ash nutrients; 1 names nutrients (potassium, calcium, phosphorus) that ash can return to the soil and says they may support subsequent growth; 1 explains that frequent or intense fires can increase nutrient loss and impede recovery; 1 makes a recommendation linked to local evidence and monitored fire intervals. [5 marks]
Common error to watch for: saying fire “destroys all the nutrients”. It releases them into ash; the risk is losing them to rain.